The present invention relates to a diagnostic or therapeutic catheter for performing various treatments in blood vessels and a medical tube used for endoscopes and the like. In particular, the present invention relates to a dilatation balloon catheter used for treating a stricture generated in a lumen such as a blood vessel by dilating the stricture, thereby improving the flow of blood in a peripheral side of the stricture, and a living organ dilatation catheter capable of delivering a living organ dilatation stent to a target living organ cite with a safety and a smooth operationality.
In recent years, functions of medical tubes have been significantly enhanced. Examples of such high function medical tubes include a vasodilatation balloon catheter used for percutaneous transluminal angioplasty for dilating a stricture in a blood vessel; a living organ dilatation catheter capable of delivering a living organ dilatation stent to a target living organ cite with a safety and a smooth operationality; a cerebrovascular catheter for injecting an embolizing material or a coil in an aneurysm or arteriovenous malformation caused in a cerebral blood vessel; an ultrasonic catheter capable of performing accurate observation or diagnosis for the inside of a blood vessel using ultrasonic diagnostic equipment; and an endoscope capable of performing accurate observation or diagnosis for the inside of a blood vessel, a bile duct, or a pancreatic duct using an image diagnostic equipment.
Such a high function medical tube has been required to have not only durability but also operationality allowing the tube to be inserted in a fine, complicated blood vessel rapidly, highly selectively. Specific examples of these requirements include (1) “pushability” allowing a catheter to be easily pushed by an operator so as to be inserted in a blood vessel; (2) “trackability” allowing a catheter to be smoothly advanced in a complicated meandering blood vessel along a previously inserted guide wire without damaging the inner wall of the blood vessel; (3) “torque transmission performance” allowing a rotational force applied on the proximal side of a catheter tube to be certainly transmitted to the distal end; and (4) “kink resistance” capable of suppressing occurrence of kink upon handling of a catheter before treatment, upon pushing the catheter, and upon pulling off a guide wire. Examples of the requirements for the high function medical tubes further include (1) “low-profile characteristics” realized by making the outer diameter of the tube as fine as possible for thinning a guiding wire adapted to guide the catheter to a target cite in order to reduce the physical or mental burden of a patient or for reducing a friction resistance with the wall of a blood vessel; (2) “thin-wall characteristic” realized by sufficiently ensuring the lumen of the tube so as to keep good operationality of a guide wire; and (3) “flexibility of the front portion of the catheter” for reducing damage of the wall of a blood vessel caused by the front portion of the catheter.
In this way, the high function medical tube is required to have not only the fineness and torque transmission performance but also the incompatible characteristics such as hardness and softness, and thin wall and resistance against breaking. Also, the ultrasonic catheter must satisfy a requirement to partially harden the tube. To produce catheter tubes satisfying these requirements, various techniques have been developed.
For example, most of vasodilatation balloon catheters commercially available at present have a basic structure including a shaft main body including a balloon inflation lumen and a guide wire lumen, and a balloon provided at a front portion of the shaft main body, wherein the shaft main body has a distal portion having a relatively low rigidity and a proximal portion having a relatively high rigidity. According to these balloon catheters, in a rigidity transition region positioned between the distal portion and the proximal portion of the shaft main body, shaft portions having different rigidities are connected to each other or the outer diameter or wall thickness is changed in order to smoothly change the rigidity or to prevent occurrence of kink due to stress concentration when a sharp bending force is applied thereto.
In the case of connecting the shaft portions having different rigidities, however, it fails to obtain a smooth change in rigidity, and therefore, there occurs a problem that stress is concentrated at the boundary (interface) of the connection portion, thereby tending to cause kink.
Also, there occurs a problem that in the case of advancing a vasodilatation balloon catheter along a meandering blood vessel to a stricture generated in a peripheral vascular vessel such as a coronary artery, kink is liable to occur at a front portion, adjacent to the balloon, of the shaft main body. The occurrence of such kink makes it difficult to smoothly transmit a pushing force given at the proximal end of the catheter to the distal end of the catheter and hence to push the catheter to a more peripheral vascular vessel.
To smoothly change the rigidity at the front portion, adjacent to the balloon, of a shaft main body for preventing occurrence of kink, some of commercially available vasodilatation balloon catheters are configured to gradually reduce the outer diameter or wall thickness of the front portion of the shaft main body in the direction toward the distal end. However, since the shaft is generally produced by extrusion molding, there arises a problem that an extrusion speed upon extrusion from a die, an extruded amount of a resin material, and the like must be accurately controlled to change the outer diameter or wall thickness of the shaft by extrusion molding, and therefore, the skillful technique is required for production of the shaft. Additionally, in the case of preventing occurrence of kink only by changing the outer diameter or wall thickness of the shaft, the effect of preventing occurrence of kink has a limitation.